diff --git a/input/fsh/artifact-profiles/group-definition.fsh b/input/fsh/artifact-profiles/group-definition.fsh
index 7e2cbc7..710f415 100644
--- a/input/fsh/artifact-profiles/group-definition.fsh
+++ b/input/fsh/artifact-profiles/group-definition.fsh
@@ -31,6 +31,11 @@ Description: "Represents the definition of a group of subjects, suitable for use
 * code MS
 * name 1..1 MS
 * characteristic MS
+* characteristic.value[x] MS
+* characteristic.valueReference.extension contains
+    GroupCharacteristicValueCanonical named valueCanonical 0..1 MS
+* characteristic.valueReference.extension[valueCanonical] ^short = "Instances that conform to the referenced profile"
+* characteristic.valueReference.extension[valueCanonical] ^definition = "Instances that conform to the referenced profile are included (or excluded if characteristic.exclude is true) in the cohort."
 * member MS
   * entity MS
     * extension contains 
diff --git a/input/fsh/examples/group-cohort-definition-example.fsh b/input/fsh/examples/group-cohort-definition-example.fsh
new file mode 100644
index 0000000..8308222
--- /dev/null
+++ b/input/fsh/examples/group-cohort-definition-example.fsh
@@ -0,0 +1,19 @@
+Instance: ExampleCohortDefinition
+InstanceOf: CRMIGroupDefinition
+Title: "Example Cohort Definition"
+Description: "An example cohort definition using the GroupDefinition profile"
+* type = #person
+* actual = false
+* name = "Adult Diabetes Patients"
+* characteristic[+].code = http://snomed.info/sct#64572001 "Disease (disorder)"
+* characteristic[=].code.text = "Patients with diabetes diagnosis"
+* characteristic[=].valueCodeableConcept = http://snomed.info/sct#73211009 "Diabetes mellitus"
+* characteristic[=].exclude = false
+* characteristic[+].code = http://loinc.org#30525-0 "Age"
+* characteristic[=].code.text = "Adults 18 years and older"
+* characteristic[=].valueQuantity = 18 'a' "years"
+* characteristic[=].exclude = false
+* characteristic[+].code = http://loinc.org#4548-4 "Hemoglobin A1c/Hemoglobin.total in Blood"
+* characteristic[=].code.text = "Patients with high HbA1c (>6%)"
+* characteristic[=].valueReference.extension[valueCanonical].valueCanonical = "http://example.org/fhir/StructureDefinition/high-a1c-observation"
+* characteristic[=].exclude = false
diff --git a/input/fsh/extensions/group-characteristic-value-canonical-extension.fsh b/input/fsh/extensions/group-characteristic-value-canonical-extension.fsh
new file mode 100644
index 0000000..a76a337
--- /dev/null
+++ b/input/fsh/extensions/group-characteristic-value-canonical-extension.fsh
@@ -0,0 +1,6 @@
+Extension: GroupCharacteristicValueCanonical
+Id: crmi-group-characteristic-value-canonical
+Title: "Group Characteristic Value Canonical Extension"
+Description: "Extends Group.characteristic.valueReference to support canonical references to profiles, where instances that conform to the referenced profile are included in the group characteristic."
+Context: Group.characteristic.valueReference
+* value[x] only canonical
diff --git a/oids.ini b/oids.ini
index c9d9d40..ac3bcbb 100644
--- a/oids.ini
+++ b/oids.ini
@@ -135,6 +135,7 @@ crmi-endpointConfiguration = 2.16.840.1.113883.4.642.40.38.42.80
 crmi-endpointconfigurationparameters = 2.16.840.1.113883.4.642.40.38.42.81
 crmi-referenceSource = 2.16.840.1.113883.4.642.40.38.42.82
 crmi-publishable-bundle = 2.16.840.1.113883.4.642.40.38.42.83
+crmi-group-characteristic-value-canonical = 2.16.840.1.113883.4.642.40.38.42.84
 
 [OperationDefinition]
 crmi-approve = 2.16.840.1.113883.4.642.40.38.33.1
@@ -179,6 +180,9 @@ shareable-example = 2.16.840.1.113883.4.642.40.38.11.3
 publishable-example = 2.16.840.1.113883.4.642.40.38.26.1
 shareable-example = 2.16.840.1.113883.4.642.40.38.26.2
 
+[Group]
+ExampleCohortDefinition = 2.16.840.1.113883.4.642.40.38.25.1
+
 [ImplementationGuide]
 publishable-example = 2.16.840.1.113883.4.642.40.38.27.1
 shareable-example = 2.16.840.1.113883.4.642.40.38.27.2